phenylephrine

Action and Spectrum

Actions and Spectrum: 

phenylephrine is a medication that acts as a selective alpha-1 adrenergic receptor agonist. It is used as a decongestant and vasoconstrictor to treat symptoms associated with nasal congestion, such as those caused by allergies or the common cold. 

When administered, phenylephrine binds to the alpha-1 receptors in the smooth muscles of blood vessels, causing them to constrict. This results in increased blood pressure and reduced blood flow to the nasal mucosa, which can alleviate congestion. 

phenylephrine also has some mild beta-1 adrenergic receptor activity, which can increase heart rate and contractility. However, the alpha-1 adrenergic receptor activity is more significant, and thus, the medication is primarily used for its vasoconstrictive effects. 

Overall, the action of phenylephrine is to constrict blood vessels, increase blood pressure, and reduce nasal congestion. Its spectrum of activity is primarily limited to its effects on the alpha-1 adrenergic receptors in the smooth muscles of blood vessels. 

Drug Interaction

Adverse Reaction

Frequency not defined 

Burning 

Hypertension 

Sneezing 

Anxiety 

Extravasation 

Nausea 

Headache 

Gastric irritation 

Metabolic acidosis 

Rebound congestion 

Reflex bradycardia 

Pulmonary edema 

Decreased renal perfusion 

Reduced urine output 

Black Box Warning

Black Box Warning: 

phenylephrine has a black box warning for its use in patients with severe hypertension, particularly those with hypertensive crisis. The drug can cause a sudden and potentially dangerous increase in blood pressure in these patients, leading to complications such as stroke, heart attack, or kidney damage. 

Patients with a prior history of cardiac diseases, including arrhythmias, angina, and myocardial infarction, should use phenylephrine cautiously, as the medication can increase heart rate and worsen these conditions. 

Additionally, phenylephrine should not be used in patients taking monoamine oxidase inhibitors (MAOIs) or other drugs that can increase blood pressure, as this can lead to a hypertensive crisis. 

Contraindication / Caution

Contraindication/Caution: 

Contraindication 

• Hypersensitivity: phenylephrine should not be used in patients with known hypersensitivity/allergy to the drug or its components. 
• Severe hypertension: phenylephrine can cause a sudden and potentially dangerous increase in blood pressure, particularly in patients with severe hypertension or hypertensive crisis.  
• Coronary artery disease: phenylephrine can increase heart rate and blood pressure, worsening conditions like angina or myocardial infarction. Patients with these conditions should use phenylephrine with caution. 
• Monoamine oxidase inhibitors (MAOIs): phenylephrine should not be used in patients taking MAOIs or within two weeks of stopping MAOIs, as this can lead to a hypertensive crisis. 
• Closed-angle glaucoma: phenylephrine can cause an increase in intraocular pressure; therefore, it is contraindicated in patients with closed-angle glaucoma. 
• Prostatic hypertrophy: phenylephrine can cause urinary retention and worsen symptoms in patients with prostatic hypertrophy. 
• Cardiovascular disease: Patients with a history of cardiovascular disease, including arrhythmias, should use phenylephrine cautiously, as it can worsen these conditions. 

Caution 

• Use in pregnancy and breastfeeding: phenylephrine is generally considered safe during pregnancy and breastfeeding, but caution should be exercised. Pregnant condition/breastfeeding women should consult their doctor before using this medication. 
• Use in pediatric patients: phenylephrine is only recommended for use in children under 12 with the guidance of a healthcare provider. 
• Use in elderly patients: Elderly patients might be more sensitive to the effects of phenylephrine. 
• Use with other medications: phenylephrine can interact with other medications, including beta-blockers, antidepressants, and other drugs that can increase blood pressure. Patients should inform their doctor of their medications before using phenylephrine. 
• Use with caution in patients with diabetes: phenylephrine can enhance blood glucose levels. 
• Use caution in patients with thyroid disease: phenylephrine can affect thyroid hormone levels. 
• Use caution in patients with liver or kidney disease: phenylephrine is metabolized in the liver and excreted in the kidneys. 

Pregnancy / Lactation

Pregnancy consideration:  

AU TGA pregnancy category: B2
US FDA pregnancy category: C 

Lactation:   

Excreted into human milk is Not known. 

Pregnancy category: 

• Category A: well-controlled and Satisfactory studies do not show risk to the fetus in the first/later trimester.        
• Category B: there was no evidence of risk to the fetus in animal studies, and there were not enough studies on pregnant women        
• Category C: there was evidence of risk of adverse effects in animal reproduction studies, and no adequate evidence in human studies must take care of potential risks in pregnant women.       
• Category D: adequate data with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits.        
• Category X: Drugs listed in this category outweigh the risks over benefits. Hence these categories of drugs need to be avoided by pregnant women.        
• Category N: There is no data available for the drug under this category 

Pharmacology

Pharmacology: 

phenylephrine is a sympathomimetic drug that acts as a selective alpha-1 adrenergic receptor agonist. When administered, it activates the alpha-1 adrenergic receptors in blood vessels and smooth muscles, leading to vasoconstriction and increased blood pressure.

This vasoconstrictive effect is particularly potent in the veins and capacitance vessels, leading to increased venous return and cardiac output. phenylephrine also acts on the alpha-1 adrenergic receptors in the nasal mucosa, causing vasoconstriction and reducing nasal congestion. 

Pharmacodynamics: 

Mechanism of action: The medication has a mechanism of action that involves strong alpha effects, which leads to increased peripheral vascular resistance and blood pressure. As a result, it decreases cardiac output and renal perfusion. 

Pharmacokinetics: 

Absorption 

phenylephrine can be administered via different routes, such as oral, nasal, ophthalmic, and parenteral. When administered orally, the bioavailability is low (less than 38%) due to extensive first-pass metabolism in the liver. After nasal administration, phenylephrine is absorbed rapidly through the nasal mucosa, and onset of action is usually within 15 minutes. When administered as eye drops, it is absorbed through the cornea and reaches the systemic circulation through the conjunctival vessels. 

Distribution 

phenylephrine has a moderate volume of distribution, indicating that it is distributed throughout the body. It is highly bound to plasma proteins, with a binding rate of approximately 95%. Phenylephrine can cross the placental barrier and is excreted in human breast milk. 

Metabolism 

phenylephrine is metabolized in the liver and intestines by two main pathways: MAO (monoamine oxidase) and COMT (catechol-O-methyltransferase). The major metabolite of phenylephrine is conjugated phenylephrine, which is excreted in the urine. The half-life of phenylephrine is relatively short, approximately 2-3 hours. 

Elimination and Excretion 

phenylephrine and its metabolites are excreted primarily in the urine, with a small amount eliminated in the feces. The excretion of phenylephrine is dose-dependent and varies with the route of administration. After nasal administration, approximately 90% of the dose is generally eliminated in the urine within one day. After intravenous administration, 70-90% of the dose is eliminated in the urine within 24 hours. 

Adminstartion

Administration: 

Intravenous administration 

Depending on the treated condition, phenylephrine is typically administered as a nasal spray, eye drops, or injection. The drug should be generally used as directed by a healthcare provider. 

• Nasal spray: phenylephrine spray treats nasal congestion caused by allergies or the common cold. As needed, the usual adult dose is one or two sprays in each nostril every four hours. The medication should be generally used for up to three days in a row. 
• Eye drops: phenylephrine eye drops are used to dilate the pupil for eye exams or to treat certain eye conditions, such as uveitis. The usual adult dose is one/two drops in the affected eye, repeated every five to 10 minutes as needed. The medication should be generally used for up to one day. 
• Injection: phenylephrine injection treats hypotension (low blood pressure) or shock. The medication is administered through an IV/injection under the skin. The dose, frequency of administration will depend on the patient’s condition and response to the medication. 

Patient Information Leaflet

Patient information leaflet 

Generic Name: phenylephrine 

Pronounced: [ FEN-il-EFF-rin ] 

Why do we use phenylephrine? 

phenylephrine is a medication that has several therapeutic uses. Some of the common uses of phenylephrine include: 

• Nasal congestion: phenylephrine is used as a nasal spray to relieve nasal congestion caused by allergies or the common cold. 
• Hypotension: phenylephrine treats hypotension (low blood pressure) caused by shock, sepsis, or other conditions. 
• Mydriasis: phenylephrine is used as eye drops to dilate the pupil for eye exams or certain eye conditions, such as uveitis. 
• Hypotension during surgery: phenylephrine raises blood pressure and maintains adequate perfusion to vital organs. 
• Anesthesia: phenylephrine is used during anesthesia to maintain blood pressure and prevent hypotension. 
• Vasopressor support: phenylephrine supports blood pressure in critically ill patients. 
• Cardiac arrest: phenylephrine may be used in cardiac arrest to improve blood flow and oxygenation.